Reconstruction of three-dimensional ozone fields using POAM III
during SOLVE
C. E. Randall,1 J. D. Lumpe,2 R. M. Bevilacqua,3 K. W. Hoppel,3M. D. Fromm,2 R. J. Salawitch,4W. H. Swartz,5,6 S. A. Lloyd,5 E. Kyro,7 P. von der Gathen,8
H. Claude,9 J. Davies,10 H. DeBacker,11 H. Dier,12M. J. Molyneux,13 and J. Sancho,14 Received 7 February 2001; revised 6 June 2001; accepted 6 July 2001; published 25 October 2002.
[1] In this paper we demonstrate the utility of the Polar Ozone and Aerosol Measurement
(POAM) III data for providing semiglobal three-dimensional ozone fields during the Stratospheric Aerosol and Gas Experiment (SAGE) III Ozone Loss and Validation Experiment (SOLVE) winter. As a solar occultation instrument, POAM III measurements were limited to latitudes of 63N to 68N during the SOLVE campaign but covered a wide range of potential vorticity. Using established mapping techniques, we have used the relation between potential vorticity and ozone measured by POAM III to calculate three-dimensional ozone mixing ratio fields throughout the Northern Hemisphere on a daily basis during the 1999/2000 winter. To validate the results, we have extensively compared profiles obtained from ozonesondes and the Halogen Occultation Experiment to the proxy O3 interpolated horizontally and vertically to the correlative measurement locations. On
average, the proxy O3agrees with the correlative observations to better than 5%, at
potential temperatures below about 900 K and latitudes above about 30N, demonstrating the reliability of the reconstructed O3fields in these regions. We discuss the application of
the POAM proxy ozone profiles for calculating photolysis rates along the ER-2 and DC-8 flight tracks during the SOLVE campaign, and we present a qualitative picture of the evolution of polar stratospheric ozone throughout the winter. INDEXTERMS:0340 Atmospheric Composition and Structure: Middle atmosphere—composition and chemistry; 0341 Atmospheric Composition and Structure: Middle atmosphere—constituent transport and chemistry (3334); 0394
Atmospheric Composition and Structure: Instruments and techniques; 3337 Meteorology and Atmospheric Dynamics: Numerical modeling and data assimilation;KEYWORDS:POAM, ozone, reconstruction, SOLVE, potential vorticity, data assimilation
Citation: Randall, C. E., et al., Reconstruction of three-dimensional ozone fields using POAM III during SOLVE,J. Geophys. Res., 107(D20), 8299, doi:10.1029/2001JD000471, 2002.
1. Introduction
[2] The Stratospheric Aerosol and Gas Experiment (SAGE)
III Ozone Loss and Validation Experiment (SOLVE) cam-paign was designed to investigate the processes causing O3
loss at high northern latitudes and to provide correlative data for validating SAGE III. One of the goals of SOLVE was to optimize the inference of O3 loss from satellite
observations, for those years when dedicated ground, bal-loon, and/or aircraft campaigns are not feasible. Although
the launch of SAGE III was unfortunately delayed, the Polar Ozone and Aerosol Measurement (POAM) III instrument, a satellite-based solar occultation instrument with latitude coverage similar to the planned SAGE III measurements, was (and still is) operational. During the SOLVE campaign, POAM III provided daily stratospheric profiles of ozone, water vapor, nitrogen dioxide, and aerosol extinction in the Northern Hemisphere (NH) from 63N to 68N with about 1 km vertical resolution. These measurements are being
1
Laboratory for Atmospheric and Space Physics, University of Colorado, Boulder, Colorado, USA.
2
Computational Physics, Inc., Springfield, Virginia, USA. 3
Naval Research Laboratory, Washington, D. C., USA. 4
Jet Propulsion Laboratory, Pasadena, California, USA. 5
Applied Physics Laboratory, Johns Hopkins University, Laurel, Maryland, USA.
6
Department of Chemistry and Biochemistry, University of Maryland, College Park, Maryland, USA.
Copyright 2002 by the American Geophysical Union. 0148-0227/02/2001JD000471
SOL 42
-
17Finnish Meteorological Institute Sodankyla¨ Observatory, Sodankyla¨, Finland.
8
Alfred Wegener Institute for Polar and Marine Research, Potsdam, Germany.
9
Hohenpeissenberg Observatory, Deutscher Wetterdienst, Hohenpeis-senberg, Germany.
10
Environment Canada, Downsview, Ontario, Canada. 11Royal Meteorological Institute of Belgium, Brussels, Belgium. 12
Deutscher Wetterdienst Meteorological Observatory Lindenberg, Lindenberg, Germany.
13
Meteorological Office, Wokingham, UK. 14
used to investigate the polar processes responsible for O3
loss during the 1999/2000 NH winter [e.g., Hoppel et al., 2002;Bevilacqua et al., 2002].
[3] It is now well established that the 1999/2000 NH
polar vortex was unusually cold, with temperatures often below the threshold for forming polar stratospheric clouds [Manney and Sabutis, 2000]. O3decreases inside the polar
vortex of 0.04 ± 0.01 ppmv d1 were observed in Micro-wave Limb Sounder (MLS) data from early February [Santee et al., 2000], and O3 chemical loss of more than
70% by the end of March has been inferred from ozone-sonde data at Ny A˚ lesund, Spitsbergen (79N, 12E) [Sinnhuber et al., 2000]. Nevertheless, the precise mech-anisms controlling the magnitude of the O3loss have yet
to be elucidated in detail. Ideally, a campaign such as SOLVE would be supported by global satellite measure-ments, with the ground-based, balloon, and aircraft meas-urements providing detailed but localized information, and the satellite providing measurements to place this informa-tion into a more global context. Although the Total Ozone Mapping Spectrometer (TOMS) instrument provides an excellent near-global map of column O3, vertically
resolved measurements are often preferable for mechanistic studies. Unfortunately, no instrument capable of providing global O3profiles with high vertical resolution was
opera-tional throughout the SOLVE campaign (although the MLS was operational for 9 days in February and March [Santee et al., 2000]).
[4] In an effort to improve this situation, we have
reconstructed daily, semiglobal (NH only), vertically resolved O3 fields from the POAM data. The technique
by which this was accomplished, which we refer to as potential vorticity (PV) mapping, was established more than a decade ago for use with Limb Infrared Monitor of the Stratosphere [Butchart and Remsberg, 1986] and ER-2
[Schoeberl et al., 1989] data. This technique makes it
possible, under certain conditions, to calculate mixing ratios over a much wider range of geographic locations than were actually observed. In this paper we describe the PV map-ping technique as applied to the POAM III data, validate the results, and show how these results are useful for the SOLVE objectives.
[5] The premise behind the PV mapping technique is that
PV is a conserved quantity during adiabatic transport, so it is often used as a tracer of atmospheric motions. Since O3in
the winter stratosphere is dynamically controlled, a single, well-defined relationship defines its correlation with PV across the polar vortex anywhere on a given potential temperature (q) surface at any given point in time [e.g.,
Leovy et al., 1985;Allaart et al., 1993]. If this relationship is determined by measuring O3 over a sufficient range of
PV/qspace, it can thus be used to derive O3mixing ratios at
geographic locations outside the actual measurement field, as long as the PV andqvalues at those locations are known. The technique has been incorporated into studies of vortex processes in both hemispheres [Schoeberl et al., 1989;Lait et al., 1990;Manney et al., 1998, 1999], and the underlying concepts have been used to improve satellite data intercom-parisons [Manney et al., 2001;Redaelli et al., 1994]. This paper describes its first application with POAM III O3data.
POAM III routinely measured O3profiles over a wide range
of PV during the SOLVE campaign (see section 2). Taking
advantage of the PV analyses from the UK Meteorological Office (UKMO) [Swinbank and O’Neill, 1994], we were able to reconstruct O3profiles on the NH UKMO grid, as
described in section 3. We evaluated the NH gridded O3
‘‘proxy’’ product by interpolating the profiles vertically and horizontally to the locations of correlative measurements, to which we compared the proxy profiles. These comparisons are described in section 4. The initial motivation for performing and validating the PV mapping with POAM III data during SOLVE was to derive O3profiles above the
SOLVE aircraft measurements. These profiles could then be used to determine solar flux transmissions for theoretical calculations of photolysis reaction rates. This application of the proxy O3data is the subject of section 5.
2. POAM III Data
[6] Each day, approximately 15 POAM observations,
separated by25 in longitude, are made around a circle of approximately constant latitude in the Northern Hemi-sphere (NH) at local sunset. The average latitude of the observations on each day from 1 November 1999 through 30 April 2000 is shown in Figure 1. At each measurement location, POAM measures profiles of O3 (10 – 60 km),
aerosol extinction at five wavelengths from 353 to 1020 nm (10 – 30 km), NO2(20 – 40 km), and H2O (10 – 45
km). In this paper we focus on the version 3.0 POAM III O3 data. Preliminary validation of an earlier version of
POAM III O3was described byLucke et al. [1999]. More
recent analyses with version 3.0 have been completed by
Lumpe et al. [2002] and Randall et al. (Validation of
POAM III O3: Comparison to ozonesonde and satellite
data, submitted toJournal of Geophysical Research, 2002) (hereinafter referred to as Randall et al. (submitted manu-script, 2002)). These show that on average, POAM III O3
profiles in the NH agree to better than 10% with correla-tive observations from 12 to 60 km.
[7] Because the vortex is often displaced from the pole in
the NH, POAM III makes measurements at a wide range of equivalent latitudes [Butchart and Remsberg, 1986] on a daily basis during the winter, even though the geographic latitude is essentially constant on a given day. For example, Figure 2 shows the PV on the 500 K potential temperature surface corresponding to every POAM measurement in the NH from 1 November 1999 through 30 April 2000. For this figure and elsewhere in the paper, we use UKMO PV analyses interpolated in time and space to the POAM measurement locations when necessary. The inner and outer vortex edge boundaries, as defined by Nash et al.[1996], are denoted in the plot. From late December through mid March, POAM sampled in the vortex core, on the vortex edge, and outside the vortex on a near-daily basis. It is this characteristic of the POAM measurements that allows the analysis described below.
[8] To illustrate how O3changes with PV, a contour plot
of the O3 field generated from measurements obtained by
POAM over a 3-day period from 24 – 26 December 1999 is given in Figure 3. Maps such as this were provided to SOLVE campaign participants on a daily basis throughout the winter. At this particular time and latitude, measure-ment locations at longitudes of about 330E to 60E were inside the vortex (in-V), with longitudes near 180 well outside the vortex (out-V), and longitudes near 120E and 300E on the edge of the vortex (edge-V). This is quite typical for the vortex structure and location in the NH. Since O3is in dynamical control at this time and latitude,
mixing ratios follow the vortex structure. At all altitudes above about 500 K, O3 mixing ratios are significantly
higher outside the vortex than inside; this results largely from transport of O3-rich air from lower latitudes to the
polar region outside the vortex [Randall et al., 1995]. Inside the vortex, air parcels cannot mix as freely with the lower latitude air, so mixing ratios remain lower than outside the vortex. Near 450 K, where the vertical gradient
in the O3 profile is larger than at the higher altitudes, O3
mixing ratios inside the vortex are slightly higher than outside. This is due to enhanced diabatic descent inside the vortex. Because O3 mixing ratios increase with altitude
here, air parcels descending inside the vortex to 450 K increase the O3mixing ratios to values above those outside
the vortex, where descent occurs less rapidly and with more horizontal mixing [e.g.,Randall et al., 1995;Manney et al., 1995a, and references therein].
[9] Whereas Figure 3 illustrates the O3 variation with
respect to the vortex that was observed in late December, Figure 4 presents the temporal variation in O3 that was
observed at different locations with respect to the vortex over the course of the winter. This figure shows the daily average POAM III O3mixing ratios segregated according to
position with respect to the vortex (e.g., inside, outside, or on the edge) using theNash et al.[1996] vortex definition. Although these observations were all acquired within the fairly narrow latitude band depicted in Figure 1, they illustrate some interesting features of the changes in vortex distribution of O3during the winter at these latitudes. For
instance, at 550 and 600 K, in-V mixing ratios are persis-tently lower than out-V mixing ratios, for the reasons stated above relating to poleward transport of high O3mixing ratio
air from lower latitudes. At 450 K in December, in-V O3is
more than 50% higher than out-V O3. Again, this was
explained above, and results from enhanced diabatic descent inside the vortex. However, in-V O3mixing ratios at 450 K
begin to decline steeply by mid February, so that by early March they are as low as out-V mixing ratios. This is the
Figure 2. Potential vorticity of the NH POAM measure-ments from 1 November 1999 through 30 April 2000. The inner and outer boundaries of the vortex edge region are denoted in blue and red, respectively.
Figure 3. Representative contour map made from POAM III O3 measurements from 24 to 26 December 1999 at a
signature of chemical O3 loss, and is discussed in more
detail byHoppel et al.[2002]. By early March, even edge-V O3is declining at 450 K. Similar declines in in-V and
edge-V O3are also evident at 500 K. Another interesting feature
is that until about mid January, edge-V mixing ratios at 500 K are higher than both in-V and out-V. We believe that this can be explained primarily by a variation across the edge of the vortex in the O3 profile vertical gradient near 500 K.
Examination of POAM III profiles in October and Novem-ber reveals that edge-V and out-V O3mixing ratio profiles
exhibited a steep gradient from 400 to 600 K. Enhanced diabatic descent on the edge of the vortex would have resulted in higher edge-V O3than out-V, just as at 450 K.
However, whereas in-V O3mixing ratios followed a
sim-ilarly steep gradient from 400 to 500 K, they were roughly constant near 3.0 ppmv or less above about 500 K. Thus enhanced diabatic descent inside the vortex produced little change in the in-V O3mixing ratios at this time, resulting in
edge-V O3 mixing ratios that were higher than both in-V
and out-V. There may also be a contribution from faster diabatic descent along the edge of the vortex compared to inside. Reverse trajectory calculations performed elsewhere (G. Manney, private communication, 2001) showed that air parcels at 500 K on 5 January would have descended10 K further on the edge of the vortex than inside during the preceding 40 days.
3. Method
[10] As mentioned above, the fact that PV is conserved
during adiabatic transport allows us to use it to follow the
motion of tracers (such as O3 under many conditions) on
isentropic surfaces. This concept can be applied to approx-imate O3at geographic locations distant from actual
meas-urements, as long as the measurements themselves adequately constrain the relationship between PV and O3,
and the PV values at the remote locations are well known [e.g.,Schoeberl et al., 1989]. As shown above, POAM III measurements span a wide range of PV values daily throughout the NH winter and clearly document variations in O3expected from the changing PV. For every day during
the SOLVE campaign, we thus calculated an analytic (quadratic) expression relating PV to O3using the POAM
III O3 profiles and the UKMO PV values interpolated in
time and space to the POAM measurement locations. In practice, we actually used O3and PV data corresponding to
the 7-day interval centered on the day of interest. We found by trial and error that this interval length corresponded to the optimum balance for defining the PV/O3 relation.
Including more days introduces error due to varying PV/ O3correlations, particularly in times of rapid vortex
evolu-tion. Including fewer days results in poorer statistics in general, the quadratic fits in these cases were qualitatively similar to the 7-day analyses but suffered from more noise. For each day during the SOLVE winter we then applied this relation to the daily 1200 UT NH UKMO PV field to generate proxy O3 mixing ratios on the same latitude/
longitude grids as the UKMO data (for this work these grids spanned the NH in 2.5-degree increments in latitude and 3.75-degree increments in longitude).
[11] Our method is illustrated in Figure 5 for 1 January
2000 at 650 K. Figure 5a shows the POAM III O3mixing
ratios from 29 December through 4 January plotted against the UKMO PV interpolated to the POAM III measurement locations on the 650 K surface. For this altitude and time, high PV values correspond to the lowest values of O3, and
low PV values correspond to the highest values of O3, since
O3 outside the vortex is higher than inside, as discussed
above. Superimposed on the data is a quadratic fit. We calculated a proxy O3field for this day by multiplying the
650 K UKMO PV grid for 1 January by the quadratic coefficients defining the fit in Figure 5a. Figure 5b shows a contour map of the UKMO PV, clearly depicting the vortex as having an oval shape with its long axis oriented along 90E – 270E longitude and its center displaced from the pole toward Greenland and Scandinavia. Over the 7-day period from 29 December to 4 January the POAM measure-ments spanned the latitude circle near 63, in fairly regular longitude intervals of about five degrees. The measurements occurred well outside and inside the vortex, missing only the region with the very highest values of PV. The proxy O3
field, calculated from the PV field in Figure 5b and the quadratic coefficients defining the fit in Figure 5a, is plotted in Figure 5c. As expected from the monotonic PV/O3
relation in Figure 5a, the O3field is essentially the reverse
of the PV field, with low O3inside the vortex, and high O3
outside the vortex.
[12] Extending this illustration to other days, Figure 6
shows the POAM III O3 mixing ratios at 500 K and
quadratic PV/O3 fits for four different days during the
SOLVE campaign. This figure illustrates the gradually changing PV/O3 relation over the course of the winter.
Although similar information about the data can be derived
Figure 4. Daily average POAM III O3mixing ratios inside
from Figure 4, we focus here on the quadratic fits to the data. The most salient point about this figure is that for all of these days, a quadratic fit appears to match the data quite well, on average. On 20 December, edge and in-V mixing ratios are higher than out-V, due to enhanced diabatic descent inside the vortex. The fit shows a slight enhance-ment of edge mixing ratios over in-V mixing ratios, but this is somewhat uncertain since, as shown in Figure 2, only a small fraction of the POAM measurements at this time occurred inside the inner edge of the vortex. Thus extrap-olation of this quadratic to substantially higher values of PV is expected to be less certain than, for instance, extrapola-tion to lower values of PV. By the end of January, the enhancement of edge O3 mixing ratios over those both
outside and inside the vortex is clear, the result of enhanced diabatic descent on the edge bringing down O3-rich air. By
late February the fits indicate mixing ratios inside the vortex that are significantly less than outside, a result expected only in the presence of chemical O3 loss. On 20 March,
even though POAM sampled a wide range of PV, fewer points define the quadratic inside the vortex, suggesting higher uncertainty for the fit at this time.
[13] Applying the fits shown in Figure 6 to the UKMO PV
fields, we generated the proxy O3maps shown in Figure 7.
Overall, these maps are consistent with the interpretation of the plots at the POAM latitudes discussed above. That is, areas of highest O3in December through February form a
collar near the vortex edge, where descent of O3-rich air
dominates. The areas of lowest O3in February lie inside the
vortex, and signify chemical O3loss during the winter. On 20
March, the vortex was elongated and split into two areas of high PV (and relatively low O3), resulting in the double-lobed
appearance to this map. These maps also illustrate, however, the potential for error when using the mapping technique to infer O3 at latitudes far from the original measurements.
Consider, for instance, the map for 20 January 2000. The apparent intrusion of air with high O3mixing ratios from the
vortex edge to the pole near Greenland is an artifact due to anomalous structure in the UKMO PV field for this day.
Indeed, the proxy O3mixing ratio at 500 K on 20 January,
interpolated to the location of Eureka (79.9N,85E), was higher by about 15% than the sonde measurement for that day.
[14] At the other extreme, the very low (2.2 ppmv)
proxy O3mixing ratios on 20 January near 80N latitude are
also an artifact and are lower than actual measurements, for instance at Ny A˚ lesund (see section 4). These low mixing ratios result from an extrapolation of the PV/O3relation to
higher PV values and latitudes than were observed. The
43 64 84 104 124 144 165 185 205 225 246 266 286 306 326
(b)
3.43.63.8 4.0 4.2 4.4 4.7 4.9 5.1 5.3 5.5 5.7 6.0 6.2 6.4
(c)
50 100 150 200 250 300 350UKMO PV (10-6 K m2 kg-1 s-1) 3.5
4.0 4.5 5.0 5.5 6.0
O 3
(ppmv)
( ) Data
Fit
(a)
Figure 5. (a) POAM III O3mixing ratios at 650 K from 29 December through 4 January 2000 (red
asterisks), plotted against the UKMO PV interpolated in time and space to the POAM measurement locations. Superimposed is a quadratic fit to the data. (b) UKMO PV field on 1 January 2000 on the 650 K potential temperature surface. Latitude lines are drawn at 30N and 60N, and east longitudes increase counterclockwise from 0 on the right. POAM measurement locations from 29 December 1999 to 4 January 2000 are denoted by the black dots. Solid (dashed) white contours denote the geographic boundaries inside (outside) of which the PV values were higher (lower) than those sampled by POAM. (c) The proxy O3field for 1 January 2000, calculated as described in the text. The color scales refer to (b)
PV (106m2kg1s1K) and to (c) O3mixing ratio (ppmv).
primary reason for this is that because of the dynamically induced higher O3on the edge of the vortex, the mapping
technique causes O3 to monotonically decrease at higher
values of PV that are not sampled by POAM, rather than to level off to some extent inside the vortex. Using higher-order polynomials for the PV/O3fits can alleviate this type
of problem somewhat but introduces other artifacts into the analysis. This effect is exacerbated by the fact that the return of sunlight to the POAM measurement latitude (64N) in January caused some chemical loss at 500 K (see Figure 4
and Hoppel et al. [2002]) inside the vortex. Even though
such loss could not yet have occurred at the higher latitudes still in darkness, the mapping technique generalizes it to the entire vortex and in fact extrapolates to even lower O3
values at the higher PV values. In the next section we explore in detail the effects of such errors on the validity of the reconstructed fields.
4. Validation of the Method
[15] To validate the PV mapping technique with POAM
data, we have extensively compared the proxy O3profiles
generated using the method above to profiles obtained from balloon-based electrochemical concentration cell and Brewer-Mast ozonesondes and the Halogen Occultation Experiment (HALOE). Comparisons were made by inter-polating the proxy O3 horizontally and vertically to the
correlative measurement locations. These comparisons included locations both well north and well south of the actual POAM III measurement locations and both outside and inside the polar vortex. Ozonesonde profiles were
obtained from a sonde network operating within the frame-work of the SOLVE/Third European Stratospheric Experi-ment on Ozone (THESEO-2000) project. For this work we used data from 29 stations in Europe, North America, and Russia. Station locations and the number of profiles used from each are listed in Table 1. All data incorporated in our analysis have been quality controlled in real time during the SOLVE campaign by daily visual inspection of profiles. The time series data from Ny A˚ lesund (see below) have also passed a more rigorous, postmission quality control process. HALOE version 19 O3 data were obtained from
the HALOE home page (http://haloedata.larc.nasa.gov/). The O3profiles were placed on potential temperature grids
using the temperatures and pressures provided with the sonde (measured by radiosonde) and HALOE (obtained from the National Centers for Environmental Prediction) data sets.
[16] Figure 8 shows representative comparisons between
individual ozonesonde profiles at three different locations and the proxy O3 profiles (determined by interpolation of
the proxy O3 field on the UKMO grid to the sonde
location). For this example we have chosen to show results from stations that were roughly 14N (Ny A˚ lesund), 17S (Hohenpeissenberg), and 37S (Izana) of the POAM meas-urements. In general, the agreement with the sondes is excellent, with the proxy even capturing the steep lower stratospheric gradient in the O3 profile at Izana (28.4N).
Figure 7. As in Figure 5c, but corresponding to the plots in Figure 6.
Table 1. Ozonesonde Stations Used in the Statistical Validation Analysisa
Station Latitude Longitude Number of Comparisons
Aberystwyth 52.40 4.10 5
Alert 82.50 62.3 8
Andoya 69.30 16.11 6
Churchill 58.74 94.00 6
De Bilt 52.10 5.18 7
Stonyplain 53.55 114. 5
Eureka 79.99 85.9 17
Gardermoen 60.11 11.04 3
Goose Bay 53.18 60.2 4
Hohenpeissenberg 47.80 11.00 27
Izana 28.46 16.2 2
Jaegersborg 55.77 12.53 1
Jokioinen 60.80 23.50 12
Lerwick 60.13 1.18 22
Lindenberg 52.13 14.07 6
Legionowo 52.40 20.97 15
Ny A˚ lesund 78.93 11.95 29
Orland 63.42 9.24 14
Payerne 46.80 6.95 30
Prague 50.02 14.45 12
Keflavik 63.97 22.60 4
Resolute 74.71 94.90 12
Salekhard 66.70 66.70 10
Scoresbysund 70.50 22.00 10
Sodankyla 67.39 26.65 19
Thule 76.53 68.70 5
Uccle 50.80 4.35 23
Valentia 51.93 10.20 6
Yakutsk 62.03 129.60 5
Total 325
aThe number of comparisons from each station that were included in the
The discrepancy above 700 K in the Izana comparisons is primarily due to the fact that at this low latitude and these high altitudes, O3is no longer a passive tracer.
[17] To quantify the sonde results, we have carried out a
statistical analysis, calculating the average differences between the proxy and the sonde profiles for each of the measurements listed in Table 1. Figure 9 shows the average difference profile for these comparisons, as well as the individual differences and standard deviation of the mean (which is equivalent to the uncertainty in the mean). These results show that for the early to midwinter data included here, the proxy O3profiles on average agree with the sondes
to better than 5% below about 800 K. This agreement is particularly noteworthy given the large range of sonde locations compared to the relatively localized POAM meas-urement latitudes. Approximately 4.4% of the comparisons shown in Figure 9 include proxy O3data that were derived
from an extrapolation of the PV/O3quadratic fit beyond the
range of PV values actually sampled by POAM (75 points out of 1720). The comparisons including these extrapolated points are fairly evenly distributed among the entire set of comparisons and do not significantly affect the overall averages.
[18] To better understand the latitude dependence of the
quality of the proxy profiles, we have compared the proxy O3to more than 900 O3 profiles measured by HALOE at
the latitudes and times shown in Figure 10. The latitude dependence of the differences between HALOE and the proxy O3is shown in Figure 11 for four different potential
temperature levels. These comparisons show that between 500 and 850 K the proxy O3 generally agrees with the
HALOE data remarkably well at latitudes poleward of 30N (see below) but more poorly at equatorial latitudes. The larger differences at the lower latitudes probably have two causes. First, increasing uncertainty in the UKMO PV
field at these latitudes is likely to contribute to errors in the PV/O3 analysis. Second, these latitudes correspond to
PV values well outside the range sampled by POAM, where the quadratic relation may no longer hold (note that comparisons where the proxy O3was determined from an
extrapolation of the PV/O3 quadratic fit beyond the PV Figure 8. Representative examples of individual profile
comparisons between the proxy O3interpolated to the sonde
location (red, pluses) and the sonde profile (black) at Ny A˚ lesund (Ny), Hohenpeissenberg (Ho), and Izana (Iz), on the dates (yymmdd) shown in each panel.
Figure 9. Statistical results for all ozonesonde compar-isons between 22 November 1999 and 1 February 2000 shown as the average difference profile (solid line with dots) and the standard deviation of the mean (dotted lines), with the individual differences overplotted as red points (black crosses denote individual differences where the proxy O3
was derived from an extrapolation of the PV/O3quadratic
fit beyond the range of PV values actually sampled by POAM). The number of comparisons included at each potential temperature level is given on the right vertical axis.
range sampled by POAM are denoted in black). At 650 K and above the results at the lower latitudes may also be affected by the fact that increasing sunlight will cause O3
to transition away from a dynamically controlled situation
[Garcia and Solomon, 1985], increasing the error in the
PV/O3 analysis. Although agreement is worse at 1250 K
than at the lower altitudes, it is still quite reasonable poleward of 30N.
[19] To quantify these comparisons, Figure 12 shows the
statistical results for all events (724) poleward of 30N. Comparisons including proxy O3 derived from an
extrap-olation of the PV/O3 quadratic fit beyond the PV range
sampled by POAM constitute about 20% of the data points at latitudes poleward of 30N; their removal does not significantly alter the conclusions stated here. Like the sonde comparisons, agreement is impressive, with differ-ences often less than 5% below 1100 K. The differdiffer-ences increase at the highest altitudes, most likely because of the lack of dynamical control at these altitudes as sunlight returns to the polar region. The large differences at 400 K in part reflect real differences between the POAM and HALOE data which have not yet been resolved (Randall et al., submitted manuscript, 2002). However, near 400 K the documented differences between POAM and HALOE are only at the 10% level, and cannot entirely explain either the average differences seen in Figure 12, or the marked increase in the variability of the comparisons at 400 K. We believe the deterioration in the comparisons at 400 K may result from increased mixing of air parcels at and below this altitude, where the effective diffusivity is generally higher than at higher altitudes [Haynes and Shuckburgh, 2000]. Variable small-scale mixing could change the PV/ O3 relationship as a function of geographic location, so
that the fit derived from the POAM data would not necessarily apply to the location of the HALOE (or sonde) measurements. This would suggest that for the SOLVE winter the lower altitude limit for the PV mapping technique employed here is around 400 – 450 K. Confirm-ing this speculation requires more investigation and is beyond the scope of this paper.
[20] To probe more deeply into the quality of the PV/O3
reconstruction at latitudes poleward of the POAM measure-ments, and to evaluate the proxy O3in regions of chemical
O3 loss, we have compared in detail the proxy O3 to
ozonesonde measurements made at Ny A˚ lesund. At 78.9N and 12E this station is often located under the center of the NH vortex, where one might expect O3loss to
maximize. Indeed, as noted earlier, O3 loss of more than
70% during the SOLVE winter has been inferred above Ny A˚ lesund [Sinnhuber et al., 2000]. Figure 13 shows the evolution of O3 mixing ratios measured by sonde above
Ny A˚ lesund at four different potential temperature levels between 450 and 750 K from late November through April. Superimposed are the proxy O3values, interpolated to the
latitude and longitude of Ny A˚ lesund. Throughout most of the winter, at all of these potential temperature levels, the agreement is remarkable, with mean differences ranging from about +5% to7%. These results indicate that even at latitudes significantly poleward of the POAM measure-ments, and well inside the vortex, the PV mapping yields reasonable O3values. In particular, the proxy field captures
the variations in O3at 450 K until early March and at 500 K
until late March, including the decline caused by chemical loss processes. There are two noteworthy regions of dis-agreement. At 450 and 500 K, proxy O3values at the end of
January and beginning of February are generally somewhat lower than the sonde data. As discussed above with regard
Figure 11. Latitude dependence of the differences be-tween HALOE and the proxy O3for events noted in Figure
10, at the potential temperature levels denoted in each panel. Comparisons including proxy O3 derived from
extrapola-tion of the PV/O3 fit beyond the range of PV sampled by
POAM are indicated in black; all other comparisons are indicated in red.
to Figure 7, this results from errors in the in-V reconstruc-tion stemming largely from the fact that the air parcels sampled by POAM have been exposed to more sunlight, and thus more chemical processing leading to O3 loss,
than air over Ny A˚ lesund, even if they are at similar equivalent latitudes. In two cases, this is compounded by an extrapolation of the PV/O3 curve beyond the range of
PV sampled by POAM. This comparison thus emphasizes the need for caution when interpreting the proxy O3results
in regions where geographic gradients due to photochem-istry are significant, particularly if the proxy is derived from extrapolations beyond the sampled range of PV. The other notable disagreement occurs at 450 K near day 90, where proxy O3 is significantly higher than sonde O3. At
this time, POAM was sampling primarily on the edge of the vortex, and the mapping thus failed to capture the morphology of the substantial O3 loss that occurred at
higher equivalent latitudes. Furthermore, the vortex was evolving rapidly at this time, increasing the uncertainty in the PV mapping analysis. Note, however, that the increase in O3near day 80 (20 March), as the vortex shifted away
from Ny A˚ lesund, was captured fairly well by the PV/O3
analysis.
[21] The comparisons presented here show that overall
the proxy O3 profiles are in excellent agreement with
correlative observations and can be used extensively for
scientific investigations. Caution is required, however, when there are significant errors in our knowledge of the PV/qfields, or in our knowledge of the PV/O3relation. The
latter error, which is the most prevalent, can arise for a number of different reasons. First, this will often result when the range of PV sampled by the instrument is too narrow to adequately extrapolate outside this range. Sec-ond, the PV/O3relation may not follow closely enough the
quadratic curve that we use to define it, instead being better defined by another analytic form. Third, if the PV/qfield is changing rapidly (e.g., through diabatic processes), the PV/ O3 relation defined by a 7-day period will average over
these PV variations. Fourth, it may simply be inappropriate to assume a single (quadratic or otherwise) PV/O3relation.
This will be the case, for instance, when O3 is in
photo-chemical control and is thus not expected to strictly correlate with PV. For example, we expect the analysis to work less well in the middle to upper stratosphere in summer, and also in the presence of the anticyclonic low O3 pockets that occur in the winter middle stratosphere
[Manney et al., 1995b; Nair et al., 1998; Morris et al., 1998]. For the latter situation there may be a perfectly valid quadratic that describes the PV/O3 relation everywhere
except near the low O3pockets, where the proxy O3would
overestimate the observed O3. Note, however, that even in
the presence of chemical changes, such as polar O3loss, the
mapping technique will produce valid results as long as O3
and PV are well correlated within the time period of the analysis, and as long as the observations fulfill the other requirements such as adequate sampling of the PV/q field (e.g., Figure 13).
5. Application of the Method
[22] The results above confirm the validity of the PV
mapping technique for deriving proxy O3values from the
POAM III data at most times and locations during the NH winter poleward of 30N. These results can be used for a variety of purposes and are particularly relevant in times (such as the SOLVE winter) when high vertical resolution, global, O3measurements are lacking. In general, using the
proxy O3will improve analyses that rely on climatological
profiles for lack of actual data. For instance, the proxy O3
data have been used to initialize calculations for inves-tigations of O3 photochemical loss during the winter
[Hoppel et al., 2002] and can be used to improve satellite data retrievals which require a priori O3 profiles, such as
those from the TOMS instrument. When combined with data from other instruments such as HALOE or SAGE, the analysis can be improved at the lower latitudes. We are currently using this strategy as one means of generating global stratospheric O3 fields for inclusion in the Navy’s
operational weather prediction system (NOGAPS [Hogan
and Rosmund, 1991]). In this section we describe the
application of POAM PV mapping results to calculations of photolysis rates relevant to SOLVE investigations.
[23] One of the primary goals of the SOLVE campaign
was to investigate O3 loss processes using the numerous
measurements of stratospheric species along the DC-8 and ER-2 flight paths. To put those measurements into the context of a detailed photochemistry scheme requires knowledge of the rate coefficients for the relevant photolytic
3
4
5
6
7
750 K
2
3
4
5
6
650 K
1
2
3
4
5
500 K
-50
0
50
100
Days Since 1 January 2000
0
1
2
3
4
450 K
Ozone Mixing Ratio (ppmv)
Figure 13. Evolution of O3 mixing ratios measured by
ozonesonde over Ny A˚ lesund (pluses), at the different potential temperature levels noted in each panel, compared to the proxy O3derived for the location of this station (open
circles). Proxy O3 data derived from extrapolation of the
PV/O3 quadratic fit beyond the range of PV sampled by
reactions; i.e., thej values. The jvalues can be calculated most directly if one measures the solar actinic flux that is transmitted through the atmosphere to the aircraft location from all directions, at the appropriate wavelengths. This is accomplished by the Scanning Actinic Flux Spectroradiom-eter (SAFS) instruments [Shetter and Mu¨ller, 1999] on the DC-8 for 15 molecules of interest. A more indirect deter-mination of thejvalues is to measure the O3column above
the aircraft and to use this information to deduce the transmission through the atmosphere of the radiation responsible for the photolysis. The principal sources of overhead O3information during previous ER-2 campaigns
have been the in situ Composition and Photodissociative Flux Measurement (CPFM) [McElroy, 1995] and the TOMS satellite measurements (from which a climatological tropo-spheric column must be subtracted) [McPeters et al., 1998]. A drawback to using these measurements, however, is that they become much less reliable or unavailable at high solar zenith angles (SZAs). Thus accurately determining O3
columns over the ER-2 at high SZAs was one of the primary motivating factors for applying the PV mapping technique to the POAM III data.
[24] The POAM III reconstructed O3 fields have been
used to create consistent j value data sets for the entire campaign, independent of limitations at high SZAs. This has been done independently by two different groups, at the Applied Physics Laboratory (APL) and at the Jet Propulsion Laboratory (JPL). In order to calculate accurate
j values, it is necessary that the reconstructed O3 at and
above the aircraft flight track be accurate. The validation discussion above showed that statistically the recon-structed profiles interpolated to ozonesonde and HALOE
measurement locations compared very well to the obser-vations. We investigated the reliability of the PV mapping results for determining O3 at the aircraft location by
comparing the proxy O3 to in situ O3measurements from
the ozone photometer on board the ER-2 [Proffitt and
McLaughlin, 1983; Richard et al., 2001]. For these
com-parisons, some representative examples of which are shown in Figure 14, the proxy O3 was interpolated
horizontally and vertically to the ER-2 flight tracks. Figure 14 reveals excellent agreement between the proxy O3and
ER-2 observations, even during the rapid altitude changes (dips) of the aircraft, as expected from the comparisons shown above.
[25] To illustrate the reliability of the j value
tions themselves, Figure 15 compares the APL calcula-tions [Swartz et al., 1999] appropriate for the DC-8 flight on 3 March 2000 to thejvalues derived using actinic flux measurements from the SAFS measurement, for the O3!
O(1D) reaction. The j values derived from the POAM reconstruction analysis match those derived from the SAFS measurements quite well, generally agreeing to within 10% or better. Also shown are the j values determined using TOMS measurements of total ozone. These also match the SAFS determinations well, although not quite as well as the POAM-based calculations for this particular flight. It should be noted that for the TOMS calculations, climatological O3 profiles were scaled to the
TOMS total column, so that the O3 column below the
DC-8 could be subtracted off. Likewise, climatological profiles were used to extend the POAM measurements down to the DC-8 flight altitude. When averaged over the entire campaign, the APL(TOMS) calculations of j(O3) at
SZA > 85 exceeded determinations based on the SAFS data by 13 ± 3%. The APL(POAM) calculations on average agreed better with the SAFS determinations, exceeding them by only 3 ± 2%. With regard to these results, however, it is important to note that the TOMS
Figure 14. Comparison of the reconstructed O3
inter-polated to the ER-2 flight location (red) and the in situ measurements from the ozone photometer on board the ER-2 (black) during the flight on the date (yymmdd) noted in each panel. The sharp dips in the O3 measurements
correspond to rapid altitude changes by the ER-2.
Figure 15. Comparison of O3 photolysis j values
deter-mined by the APL group based on the POAM reconstructed O3 (solid) and the TOMS total column measurements
total O3 retrieval has not been optimized for the high
latitudes and SZAs encountered during the SOLVE cam-paign. At lower SZAs, APL(TOMS) and APL(POAM) provided more comparable levels of agreement with SAFS.
[26] Figure 16 demonstrates the utility of the j value
calculations based on the POAM reconstruction for ER-2 flights. In this figure we compare JPL jvalue calculations for the photolysis of Cl2O2based on column O3determined
from the POAM reconstruction and the CPFM measure-ments. We show two different derivations for the POAM reconstruction, including calculations based solely on the POAM proxy data, as well as calculations based on the proxy data scaled to the TOMS total column O3. For
the latter case, the reconstructed O3profiles are scaled such
that the total column abundance of the proxy profile, which is extended below the POAM measurements with a clima-tological profile, matches the TOMS total column. For this case, the proxy, scaled proxy, and CPFM j value determi-nations match quite well throughout most of the flight. However, at the highest SZAs, between11.5 and 14 UT, the CPFM values are unavailable. Thus the proxy determi-nation serves to fill in this time gap. Similar results are seen for other flights and otherjvalues: in general, there is good agreement between estimates of overhead ozone, and thusj
values, based on the POAM reconstruction and the CPFM data, for SZA less than about 85. For the largest SZA, however, the reconstruction with POAM data provides a more accurate method of determining jvalues than simply
relying on climatological data, as has been the practice in the past.
6. Summary
[27] For each day during the 1999/2000 winter we have
used the relation between PV and O3 mixing ratio to
calculate semiglobal (NH only) three-dimensional O3fields.
The work presented here represents the first demonstration of the PV mapping technique applied to solar occultation measurements at high equivalent latitudes over the course of an entire winter. We have extensively compared the proxy O3so generated to profiles obtained from ozonesondes and
HALOE. Comparisons were made by interpolating the proxy O3 horizontally and vertically to the correlative
measurement locations. These comparisons included loca-tions both well north and well south of the actual POAM III measurement locations, and both outside and inside the polar vortex. On average, the proxy O3 agrees with the
correlative observations to better than 5%, at potential temperatures below about 900 K, and at latitudes above about 30N (i.e., in the region where O3 is dynamically
controlled). These results demonstrate the reliability of the reconstructed global fields using the PV mapping technique. The POAM III proxy ozone fields have been used to estimate O3profiles for the computation of photolysis rates
along the SOLVE aircraft flight tracks.
[28] Finally, Figure 17 shows the proxy fields at 500 K
throughout the SOLVE winter in 5-day increments. This figure graphically illustrates the changing ozone field as dynamical and chemical processes perturb the polar region over the course of the winter. Air descending in and on the edge of the vortex causes O3mixing ratios to increase at 500
K and is responsible for the ring at the edge of the vortex that is so prominent in most of the panels. Persistent chemical O3
loss inside the vortex begins in late January at POAM latitudes and continues through March, as indicated by the transition toward the blue end of the color scale. Toward the end of March the vortex begins to break down at 500 K, and the two pockets of low ozone on 21 March coincide with the two branches of the vortex at this time. Even as late as 20 April, there are persistently low O3mixing ratios coinciding
with the highest PV values, presumably remnants of the low-O3regions which formed during the winter inside the vortex.
As noted above, detailed interpretation of the proxy fields requires caution when mechanisms responsible for ozone variability depend on factors other than equivalent latitude. In spite of this caveat, and other potential errors discussed above, the proxy fields illustrate the versatility and applic-ability of the solar occultation observations for O3 loss
investigations. Furthermore, by presenting a three-dimen-sional picture of the changing Arctic O3, they provide
information easily accessible to the general public. The proxy fields present a qualitative picture of semiglobal, vertically resolved O3variations throughout the winter in
the lower stratosphere, a picture that is not directly available from any of the currently operational satellite instruments. This method is easily extended to other winters measured by POAM II and POAM III. Ideally, POAM III data will be combined with HALOE or SAGE II to improve results at the lower latitudes, and with SAGE III measurements to improve PV sampling at the highest latitudes.
Figure 16. Comparison of Cl2O2 photolysis j values
determined by the JPL group based on the POAM reconstructed O3(green) and the POAM reconstructed O3
Figure 17. Proxy O3maps on the 500 K potential temperature level, as in Figure 7, for the dates shown
[29] Acknowledgments. This work was supported by NASA grant N00014-97-1-G018 and by the NASA Scientific Data Purchase program through contract NAS13-99031. We thank G. Manney for helpful discus-sions, R. Shetter for providing the SAFS data, and M. Rex for providing easy access to ozonesonde data during the SOLVE campaign. Version 3.0 POAM III data can be obtained from the NASA Langley Research Center EOSDIS Distributed Active Archive Center. We would like to acknowledge the following providers of ozonesonde data: V. Dorokhov (Central Aero-logical Observatory, Russia), M. Gil (Icelandic MeteoroAero-logical Office and Instituto Nacional de Tecnica Aeroespacial), I. S. Mikkelsen (Danish Meteorological Institute; Jaegersborg, Scoresbysund, Thule), Z. Litynska (IMWM, Legionowo), R. Stubi (Meteoswiss/Payerne), T. Turunen (Finnish Meteorological Institute, Sodankyla), and G. Vaughan (University of Wales, Aberystwyth).
References
Allaart, M. A. F., H. Kelder, and L. C. Heijboer, On the relation between ozone and potential vorticity,Geophys. Res. Lett.,20, 811 – 814, 1993. Bevilacqua, R. M., et al., Observations and analysis of PSCs detected by
POAM III during the 1999/2000 Northern Hemisphere winter,J. Geo-phys. Res.,107, doi:10.1029/2001JD00477, in press, 2002.
Butchart, N., and E. E. Remsberg, The area of the stratospheric polar vortex as a diagnostic for tracer transport on an isentropic surface,J. Atmos. Sci., 43, 1319 – 1339, 1986.
Garcia, R. R., and S. Solomon, The effect of breaking gravity waves on the dynamics and chemical composition of the mesosphere and lower ther-mosphere,J. Geophys. Res.,90, 3850 – 3868, 1985.
Haynes, P., and E. Shuckburgh, Effective diffusivity as a diagnostic of atmospheric transport, 1, Stratosphere,J. Geophys. Res.,105, 22,777 – 22,794, 2000.
Hogan, T., and T. Rosmund, The description of the Navy Operational Global Atmospheric Prediction Systems spectral forecast model,Mon. Weather Rev.,119, 1786 – 1815, 1991.
Hoppel, K. W., et al., POAM III observations of Arctic ozone loss for the 1999/2000 winter, J. Geophys. Res., 107(D20), doi:10.1029/ 2001JD00476, 2002.
Lait, L. R., An alternative form for potential vorticity,J. Atmos. Sci.,51, 1754 – 1759, 1994.
Lait, L. R., et al., Reconstruction of O3and N2O fields from ER-2, DC-8, and balloon observations,Geophys. Res. Lett.,17, 521 – 524, 1990. Leovy, C. B., C.-R. Sun, M. H. Hitchman, E. E. Remsberg, J. M. Russell
III, L. L. Gordley, J. C. Gille, and L. V. Lyjak, Transport of ozone in the middle stratosphere: Evidence for planetary wave breaking,J. Atmos. Sci.,42, 230 – 244, 1985.
Lucke, R. L., et al., The Polar Ozone and Aerosol Measurement (POAM) III instrument and early validation results, J. Geophys. Res., 104, 18,757 – 18,799, 1999.
Lumpe, J. D., et al., Comparison of POAM III ozone measurements with correlative aircraft and balloon data during SOLVE,J. Geophys. Res., 107, doi:10.1029/2001JD000472, in press, 2002.
Manney, G. L., and J. L. Sabutis, Development of the polar vortex in the 1999 – 2000 Arctic winter stratosphere,Geophys. Res. Lett.,27, 2589 – 2592, 2000.
Manney, G. L., L. Froidevaux, J. W. Waters, and R. W. Zurek, Evolution of microwave limb sounder ozone and the polar vortex during winter, J. Geophys. Res.,100, 2953 – 2972, 1995a.
Manney, G. L., et al., Formation of low ozone pockets in the middle strato-sphere anticyclone during winter,J. Geophys. Res.,100, 13,939 – 13,950, 1995b.
Manney, G. L., J. C. Bird, D. P. Donovan, T. J. Duck, J. A. Whiteway, S. R. Pal, and A. I. Carswell, Modeling ozone laminae in ground-based Arctic wintertime observations using trajectory calculations and satellite data, J. Geophys. Res.,103, 5797 – 5814, 1998.
Manney, G. L., H. A. Michelsen, M. L. Santee, M. R. Gunson, F. W. Irion, A. E. Roche, and N. J. Livesey, Polar vortex dynamics during spring and fall diagnosed using trace gas observations from the Atmospheric Trace Molecule Spectroscopy instrument,J. Geophys. Res., 104, 18,841 – 18,866, 1999.
Manney, G. L., et al., Comparison of satellite ozone observations in coin-cident air masses in early November 1994,J. Geophys. Res,106, 9923 – 9943, 2001.
McElroy, C. T., A spectroradiometer for the measurement of direct and scattered solar irradiance from on board the NASA ER-2 high-altitude research aircraft,Geophys. Res. Lett.,22, 1361 – 1364, 1995.
McPeters, R., et al., Earth Probe Total Ozone Mapping Spectrometer (TOMS) data products user’s guide,Rep. NASA/TP-1998-206895, NASA Goddard Space Flight Cent., Greenbelt, Md., 1998.
Morris, G. A., S. R. Kawa, A. R. Douglass, M. R. Schoeberl, L. Froide-vaux, and J. Waters, Low-ozone pockets explained,J. Geophys. Res., 103, 3599 – 3610, 1998.
Nair, H., M. Allen, L. Froidevaux, and R. W. Zurek, Localized rapid ozone loss in the northern winter stratosphere: An analysis of UARS observa-tions,J. Geophys. Res.,103, 1555 – 1571, 1998.
Nash, E. R., P. A. Newman, J. E. Rosenfield, and M. R. Schoeberl, An objective determination of the polar vortex using Ertel’s potential vorti-city,J. Geophys. Res.,101, 9471 – 9478, 1996.
Proffitt, M. H., and R. J. McLaughlin, Fast-response dual-beam UV absorp-tion ozone photometer suitable for use on stratospheric balloons,Rev. Sci. Instrum.,54, 1719 – 1728, 1983.
Randall, C. E., et al., Preliminary results from POAM II: Stratospheric ozone at high northern latitudes, Geophys. Res. Lett.,22, 2733 – 2736, 1995.
Redaelli, G., et al., UARS MLS O3soundings compared with lidar mea-surements using the conservative coordinates reconstruction technique, Geophys. Res. Lett.,21, 1535 – 1538, 1994.
Richard, E. C., Severe chemical ozone loss inside the Arctic polar vortex during winter 1999 – 2000 inferred from in situ airborne measurements, Geophys. Res. Lett.,28, 2197 – 2200, 2001.
Santee, M. L., G. L. Manney, N. J. Livesey, and J. W. Waters, UARS Microwave Limb Sounder observations of denitrification and ozone loss in the 2000 Arctic winter,Geophys. Res. Lett.,27, 3213 – 3216, 2000. Schoeberl, M. R., et al., Reconstruction of the constituent distribution and
trends in the Antarctic polar vortex from ER-2 flight observations, J. Geophys. Res.,94, 16,815 – 16,845, 1989.
Shetter, R. E., and M. Mu¨ller, Photolysis frequency measurements using actinic flux spectroradiometry during the PEM-Tropics mission: Instru-mentation description and some results,J. Geophys. Res.,104, 5647 – 5661, 1999.
Sinnhuber, B.-M., et al., Large loss of total ozone during the Arctic winter of 1999/2000,Geophys. Res. Lett.,27, 3473 – 3476, 2000.
Swartz, W. H., S. A. Lloyd, T. L. Kusterer, D. E. Anderson, C. T. McElroy, and C. Midwinter, A sensitivity study of photolysis rate coefficients during POLARIS,J. Geophys. Res.,104, 26,725 – 26,735, 1999. Swinbank, R., and A. O’Neill, A stratosphere-troposphere data assimilation
system,Mon. Weather Rev.,122, 686 – 702, 1994.
R. M. Bevilacqua and K. W. Hoppel, Naval Research Laboratory, Code 7220, Bldg. 2, 4555 Overlook Ave., SW, Washington, DC, 20375-5320, USA. ([email protected]; [email protected])
H. Claude, Hohenpeissenberg Observatory, Deutscher Wetterdienst, Albin-Schwaiger-Weg 10, 82383, Hohenpeissenberg, Germany. (hans. [email protected])
J. Davies, Environment Canada, 4905 Dufferin Street, Downsview, Ontario, Canada M3H 5T4. ([email protected])
H. DeBacker, Royal Meteorological Institute of Belgium, Ringlaan 3, B-1180, Brussels, Belgium. ([email protected])
H. Dier, DWD Meteorological Observatory Lindenberg, Am Observator-ium 12, 15864 Lindenberg, Germany. ([email protected])
M. D. Fromm and J. D. Lumpe, Computational Physics, Inc., 8001 Braddock Road, Suite 210, Springfield, VA 22151, USA. (fromm@ poamb.nrl.navy.mil; [email protected])
E. Kyro, FMI Sodankyla¨ Observatory, Ta¨htela¨ntie 71, FIN-99600, Sodankyla¨, Finland. ([email protected])
S. A. Lloyd and W. H. Swartz, Applied Physics Laboratory, Johns Hopkins University, 111000 Johns Hopkins Rd., Laurel, MD 20723-6099, USA. ([email protected]; [email protected])
M. J. Molyneux, Meteorological Office, Beaufort Park, Easthampstead, Wokingham, Berkshire, RG40 3DN, UK. ([email protected])
C. E. Randall, Laboratory for Atmospheric and Space Physics, University of Colorado, Campus Box 392, Boulder, CO 80309-0392, USA. (cora. [email protected])
R. J. Salawitch, Jet Propulsion Laboratory, MS 183-301, 4800 Oak Grove Dr., Pasadena, CA 91109, USA. ([email protected])
J. Sancho, Izana Atmospheric Observatory, La Marina, 20, P.O. Box 880, Santa Cruz de Tenerife, Spain. ( [email protected])